In dual distribution systems, pipe diameters and water residence times are reduced in potable water lines producing less deterioration in water quality, for example, by loss of disinfectant residual and increase in disinfectant by-products (DBP) concentrations. The concept was demonstrated for Briar Chapel, a master planned community, in Chatham County, N.C. Distribution system modeling showed that length-averaged pipe diameter of potable lines was reduced from 8.6 to 3.4 in. by using reclaimed water for fire protection and irrigation and to 2.8 in. when toilet flushing was added; water residence times were reduced from more than 16 h to fewer than 4 h. Capital costs were higher for the dual system than for the conventional system, however, these costs could be offset by smaller facilities for decentralized wastewater treatment and for water treatment.
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